Posted
by
samzenpus
on Thursday May 05, 2011 @12:47AM
from the dig-that-moon dept.

MarkWhittington writes "Harrison Schmitt, Apollo Moonwalker, geologist, and former United States Senator, recently presented a plan to solve the world's long term energy problems by developing fusion power fueled with helium-3 mined from the Moon. He presented this plan in a speech at Williston Basin Petroleum Conference."

We've known for ages that helium-3 is a good potential fusion fuel, and that mining the moon could be a good source of it. But we don't have fusion power plants yet, nor are we particularly close to getting them. So why talking about mining fuel that we're at least twenty years away from being able to use?

...because it's at least 20 years until the mining operation will be possible to start.

Also, think of all the nice things we got as a total by-product of the space race. Helium-3 is the tip of an iceberg. Permanent moon base, self-sustainable spacecraft to travel earth-moon on routine route, possibly fusion spacecraft propulsion, humans not only getting to the moon but going there routinely, experience in space mining in general (asteroid belt anyone?) and generally a significant leap towards making space travel easy and common.

It doesn't even have to be really profitable. It would be nice if the helium-3 deposits paid for the investment, but it's all the tech developed to get this to work, where all the REAL profit would happen.

You know... The huge one with the gravity well that holds the solar system together? What do they call that thing again? Oh yeah... Sol.

Seriously though, photovoltaics have hit and are now past grid parity. First Solar is already in the process of constructing a 2,000 megawatt solar farm in China, which is expected to produce power CHEAPER THAN COAL. This is without subsidies, tax credits or other financial BS. Another 1,700 megawatts of contracted capacity is scattered around the US, to be online by 2017.

I don't see how ferrying fusion fuel back from the moon could be cost effective compared to solar, even if it's done by automated harvesters.

...because it's at least 20 years until the mining operation will be possible to start.

Actually, that's pretty pessimistic.

The last time we went to the moon, it took around twelve years of R&D, using tech that's positively antiquated by modern standards, and with no precedent whatsoever to show that it was even possible to send a person to the moon and bring them back alive.

If we were to repeat that process now, we'd have the advantage of automation, precedent and over half a century of R&D to start with. And since we're talking about a mining operation, we could remove the human factor altogether, and rely on teleoperated machines (granted there's that three second delay to contend with, but there are workarounds). The total amount of He-3 fuel needed to make the trip worthwhile is small, and an unmanned return vehicle could use methods not suitable to human spaceflight.

Not that I wouldn't like to see more work on manned spaceflight mind you, but I think you're overestimating the amount of infrastructure needed for this kind of work.

He3+He3 gives 12.9MeV of energy per reaction. Thus 1 mol gives 619GJ, or 206 GJ per gram. Assume 1.5 GW power station would produce an average of 1GW all year. That is 31.5e15 J for the year. Assume a 50% efficiency and we need 306 kg of He3 per year. At STP that is about 2000 cubic meters of He3. Now in the Luna surface He3 is only at.01ppm. So at 100% mining efficiency we need to process 30 million tons of rock. In reality you would be very lucky to get 50% efficiency and you still need to consider how much of that He3 you need to burn to run the mining operation. So it is probably closer to 60-100million tons of Luna rock per year.

And thats for just one power station.

Now lets consider the fact that D+T fusion is not here yet and that He3 fusion is more than a 1000 times harder to do. In fact if you can run a He3 fusion plant you can run a DD fusion plant for a fraction of the cost since it is more that 10 times easier to do. Also the ash from DD is He3! It would be cheaper to have DD fusion He3 breeder reactors, than to mine the moon.

He3 is something moon fans bring up since they can't think of any other reason to go there.

I'm reminded of the sad stories about the father of the thermonuclear bomb, Edward Teller, as an old man, shuffling about the place with hand-built models, trying to sell the idea of building ever-bigger fusion weapons, oblivious to the fact that he was just being humored and smiled at, by the youngsters who by then, had realised that one would bring to bear far more destructive power with 10x1MT weapons, than with a single 10MT weapon.

It's true: everyone has a use-by date, the point where we outlive our usefulness to the world and just get in the way. That's what retirement is for. There are a myriad of reasons why strip-mining the Moon for He-3 is a dumb idea; the old man's lost his marbles and needs to quit.

This is a slight exaggeration and subject to unrealistic assumptions. Read (for example) http://en.wikipedia.org/wiki/Helium-3#Fusion_reactions [wikipedia.org] -- at reasonable efficiencies, it would require close to 80 kg of fuel to run a 1/2 GW power plant, "hand held" only if you are a pretty strong person. To provide all the electricity required to fuel all the homes in the US it would require roughly 20 tons of He3 a year. To replace ALL energy sources used by the US would require roughly 25 times that, some 500 tons a year. If we pretend they are metric tons to make the arithmetic easy, that's 5x10^5 kg, where the bare "cost" of getting off the moon is roughly 3 x 10^6 J/kg, the actual cost again many times that. And these numbers all assume that we have significantly passed break even in the fusion reaction itself, something that we currently haven't done -- if the best we can do in fusion efficiency is 10%, multiply all of these numbers by 10 (for example). Suddenly our 1 GW power plant requires 1600 kg of fuel and no, you can't carry it around.

Abundant energy on the moon is no problem -- both solar and hypothetical He3 burning give you ELECTRICITY, but electricity is nearly useless for lifting spacecraft in all models except Heinlein's imaginary mass drivers. So we either have to lift real chemical fuels from the Earth to the moon to be able to ship the stuff back or tackle an enormous engineering task on the moon -- no simple "drop a bunch of He3 scavenging robots" but building a mass driving linear accelerator long enough to accelerate payloads to 2.38 km/sec (2.8x10^ Joules/kg). Suddenly we're spending a small fortune on energy to lift the fuel back to earth. Paradoxically, if we burn hydrogen and oxygen as reaction/rocket fuel to lift it back, we will be wasting more fusion energy in the rocket fuel required to lift it back than we are gaining by lifting it.

What was that? Wasting more fusion energy than we gain? The problem is this: If we can burn He3, we can damn well burn D-D and D-T. One hydrogen atom in 6400 is Deuterium right here on Earth. One ninth of the mass of the oceans is hydrogen. Concentrating Deuterium in water (making "heavy water") is straightforward, 70 year old technology and is still done for certain nuclear power plants because it makes a better moderator than ordinary water -- it is economic to do, in other words, in spite of the fact that it isn't even a fuel (there is more energy available by perhaps and order of magnitude in the moderator than in the fission fuel load of a plant that does this, if D-D fusion were efficient at all). The ocean has a mass of 1.4x10^21 kg, or 2.4x10^16 kg of Deuterium. Allowing for higher efficiencies (it requires a higher temperature and pressure to burn He3 because of its greater charge, so it is basically certain that D-D fusion will always be more efficient than He3-anything) but lower yield per reaction as a wash, we might burn as much as 2500 metric tons worldwide per year, but let's be lavish and assume 10,000 (or 10^7 kg). That means there is enough Deuterium in the oceans to fuel world civilization at a significantly higher per capita energy consumption than we now have for a few billion years -- at least a billion before the concentration of D in the ocean is even close to being halved.

So actually, lunar mining of He3 isn't just stupid, it is insanely, massively, stupendously stupid. It is a thinly veiled attempt by a former astronaut to try to keep the enormously expensive space program funded by inventing the most vaporous of vaporware -- the illusion of cheap energy from the moon!

Of course, anyone who has actually read Heinlein knows that the same mass drivers that deliver our fuel in metric ton payloads could deliver e.g. 1 metric ton rocks instead. 1 metric ton of rock hitting the Earth at escape speed is 6x10^10 Joules of heat all released in a second at a single point of impac